Invasive, needle-like devices for positioning an array of deployable electrode elements for applying radio frequency energy to heat a target tissue structure, e.g., a tumor, are well-known. By way of one example illustrated in FIGS. 1 and 2, a radio frequency (RF) ablation probe 20, and in particular, a LeVeen Needle™ electrode, manufactured and distributed by Boston Scientific Corporation, includes a tubular deployment cannula 22 having an internal axial lumen 24 (shown in FIG. 3), which terminates at a distal opening 40, and a sharpened, tissue-penetrating distal tip 26. The cannula 22 is provided with a handle 28 to allow a physician to more easily grasp the proximal end of the ablation probe 20 when inserting the distal end into solid tissue, e.g., through the abdominal wall and liver tissue of a patient.
An array of tissue piercing electrode elements in the form of tines 30 are secured about the circumference of a tubular deployment member 32 seated coaxially within the cannula lumen 24 (shown in FIG. 3). The electrode tines 30 are formed of a substantially flat wire, each having a tissue piercing tip 34 for easy tracking through solid tissue. The tines 30 are made of a shape-memory stainless steel, and are flexible to take on a substantially linear shape when constrained in the cannula lumen 24 (shown in FIG. 3), and a curved, everting shape when deployed outside of the cannula lumen 24 (shown in FIG. 2). An output of an RF generator (not shown) is electrically coupled to the deployment member 32, which, itself, is electrically coupled to the electrode tines 30, such that an RF signal applied from the generator output is transmitted to the electrode tines 30, and to tissue in which the electrode tines 30 are deployed.
A proximal plunger 38 is fixed to the deployment member 32, such that movement of the plunger 38 relative to the handle 28 provides for alternate deployment of the electrode tines 30 out of, or into, the cannula lumen 24. More particularly, as shown in FIG. 1, prior to insertion of the sharpened distal tip 26 of the cannula 22 into body tissue, the plunger 38 is pulled back (or otherwise initially placed) in a position most proximal to the handle 28, with the electrode tines 30 completely constrained by and carried within the cannula lumen 24. While grasping the handle 28, the physician inserts the cannula 22 into the body tissue until the cannula tip 26 is located at a target tissue region TR, for example a tumor, using ultrasound or some other imaging modality (not shown) for guidance in locating the cannula tip 26.
As shown in FIG. 2, once the cannula tip 26 is at the target tissue region TR, the plunger 38 is moved toward the handle 28, so that the electrode tines 30 are deployed into the tissue region TR, taking on an everting, i.e., umbrella or mushroom shaped, formation. A patient return electrode (not shown) is also coupled to the RF generator in order to complete an electrical circuit. The return electrode is relatively large and acts as an “infinite” ground, such that substantially all of the RF energy from the generator is delivered into the tissue immediately adjacent the electrode tines 30. This mode of operation is commonly referred to as monopolar operation.
More comprehensive details of the LeVeen Needle™ device, and similar RF tissue treatment devices and their operation are disclosed and described in U.S. Pat. No. 6,575,967, which is incorporated by reference herein for all it teaches and describes.
Notably, one disadvantage of the afore-described LeVeen Needle™ device is that the delivery cannula lumen necessarily has a relatively large inner diameter and open distal end, in order to carry and deploy the electrode tines in the internal body tissue. As a result, undesirable tissue coring can occur in the delivery path as the distal tip of the cannula is moved through the tissue to the target region. In addition to the injury caused to the tissue path, such coring can also result in a compacted tissue plug jammed into the distal opening of the cannula, which may interfere with proper deployment of the electrode tines.
The Co-Access™ electrode device, manufactured and distributed by Boston Scientific Corporation, overcomes this problem, as described in detail in above-incorporated U.S. Pat. No. 6,575,967, by providing a separate obtuator for accessing the target tissue region. Such obturator devices are well-known, and have a blunt tip delivery cannula with a lumen through which a solid, tissue piercing stylet is inserted. The delivery cannula, with the stylet in place, is used to access the desired tissue region. The stylet is then withdrawn, leaving the distal opening of the delivery cannula in a target tissue region. A second blunt-tipped cannula carrying the deployable electrode tines is then inserted through the lumen of the first cannula. Deployment of the electrode tines, and operation of the Co-Access™ device is otherwise the same as for the LeVeen Needle™ device described above. While the Co-Access™ device avoids unwanted tissue coring, it requires extra components and steps for locating and deploying the electrode tines into a target tissue region.